Go webhook context update returns 400 on atomic POST

Trying to push variable updates to Cognigy.AI via Go. Docs state “context mutations require an atomic POST with strict type casting and reserved keyword verification.” Threw this at the endpoint:

{"userId": "usr_992", "variables": {"cart_total": 150, "scope": "session"}, "retain": true}

It’s throwing a 400 BAD_REQUEST with INVALID_CONTEXT_SCHEMA. Payload looks fine. Docs also mention “maximum variable size limits prevent update failure.” My Go struct matches the schema exactly. Session expiry triggers aren’t firing. Still stuck on the 400 error